Systems and methods for blood glucose sensing

ABSTRACT

A system for measuring a glucose level in a blood sample includes a test strip and a meter. The test strip includes a sample chamber or other testing zone, a working electrode, a counter electrode, fill-detect electrodes, and an auto-on conductor. A reagent layer is disposed in the testing zone. The auto-on conductor causes the meter to wake up and perform a test strip sequence when the test strip is inserted in the meter. The meter uses the working and counter electrodes to initially detect the blood sample in the sample chamber and uses the fill-detect electrodes to check that the blood sample has mixed with the reagent layer. The meter applies an assay voltage between the working and counter electrodes and measures the resulting current. The meter calculates the glucose level based on the measured current and calibration data saved in memory from a removable data storage device associated with the test strip.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. patent applicationSer. No. 10/420,995, filed Apr. 21, 2003 and is also acontinuation-in-part of U.S. application Ser. No. 10/286,648, filed Nov.1, 2002, now U.S. Pat. No. 6,743,635, issued on Jun. 1, 2004, whichapplications claim the benefit of U.S. Provisional Patent ApplicationSer. No. 60/375,017, filed Apr. 25, 2002, U.S. Provisional PatentApplication Ser. No. 60/375,019, filed Apr. 25, 2002, U.S. ProvisionalPatent Application Ser. No. 60/375,020, filed Apr. 25, 2002, and U.S.Provisional Patent Application Ser. No. 60/375,054, filed Apr. 25, 2002.Each of the foregoing utility and provisional applications is fullyincorporated herein by reference.

BACKGROUND

1. Field of the Invention

The present invention relates to electrochemical sensors and, moreparticularly, to systems and methods for sensing blood glucose levelselectrochemically.

2. Description of Related Art

Many people, such as diabetics, have a need to monitor their bloodglucose levels on a daily basis. A number of systems that allow peopleto conveniently monitor their blood glucose levels are available. Suchsystems typically include a test strip where the user applies a bloodsample and a meter that “reads” the test strip to determine the glucoselevel in the blood sample.

Among the various technologies available for measuring blood glucoselevels, electrochemical technologies are particularly desirable becauseonly a very small blood sample may be needed to perform the measurement.In electrochemical-based systems, the test strip typically includes asample chamber that contains reagents, such as glucose oxidase and amediator, and electrodes. When the user applies a blood sample to thesample chamber, the reagents react with the glucose, and the meterapplies a voltage to the electrodes to cause a redox reaction. The metermeasures the resulting current and calculates the glucose level based onthe current.

It should be emphasized that accurate measurements of blood glucoselevels may be critical to the long-term health of many users. As aresult, there is a need for a high level of reliability in the metersand test strips used to measure blood glucose levels. However, as samplesizes become smaller, the dimensions of the sample chamber andelectrodes in the test strip also become smaller. This, in turn, maymake test strips become more sensitive to smaller manufacturing defectsand to damage from subsequent handling.

Accordingly, there is a need to provide blood glucose measuring systemsand methods with features for measuring blood glucose levelsconveniently and reliably.

SUMMARY

In a first principal aspect, the present invention provides a test stripfor testing a blood sample. The test strip comprises a first substrate,a second substrate that defines a testing zone, at least four electrodesfor measuring at least one electrical characteristic of the blood samplein the testing zone, a plurality of electrical contacts electricallyconnected to the at least four electrodes, and at least one auto-onelectrical contact electrically isolated from the at least fourelectrodes. The at least four electrodes include a working electrode, acounter electrode, a fill-detect anode, and a fill-detect cathode.

In a second principal aspect, the present invention provides a method ofmaking a plurality of test strips. In accordance with the method, aplurality of test strip structures are formed on one sheet, and the teststrip structures are separated into test strips. Each of the test stripstructures includes a spacer defining a testing zone, a plurality ofelectrodes (including a working electrode, a counter electrode, afill-detect anode, and a fill-detect cathode), a plurality of electricalcontacts electrically connected to the electrodes, and at least oneauto-on electrical contact electrically isolated from the plurality ofelectrodes.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a top plan view of a test strip, in accordance with a firstexemplary embodiment of the present invention.

FIG. 2 is a top plan view of the test strip of FIG. 1, with the cover,adhesive layer, and reagent layer cut away, in accordance with a firstexemplary embodiment of the present invention.

FIG. 3 is a cross-sectional view of the test strip of FIG. 1, takenalong line 3—3, in accordance with a first exemplary embodiment of thepresent invention.

FIG. 4 is a top plan view of a test strip, in accordance with a secondexemplary embodiment of the present invention.

FIG. 5 is a top plan view of a test strip, in accordance with a thirdexemplary embodiment of the present invention.

FIG. 6 is a cross-sectional schematic view of a test strip, inaccordance with a first alternate embodiment of the present invention.

FIG. 7 is a cross-sectional schematic view of a test strip, inaccordance with a second alternate embodiment of the present invention.

FIG. 8 is a top schematic view of an array of test strip structures,which may be separated into a plurality of test strips of the type shownin FIGS. 1-3, in accordance with an exemplary embodiment of the presentinvention.

FIG. 9 is top plan view of an intermediate stage in the formation of oneof the test strip structures of FIG. 8, in accordance with an exemplaryembodiment of the present invention.

FIG. 10 is top plan view of an intermediate stage in the formation ofone of the test strip structures of FIG. 8, in accordance with anexemplary embodiment of the present invention.

FIG. 11 is top plan view of an intermediate stage in the formation ofone of the test strip structures of FIG. 8, in accordance with anexemplary embodiment of the present invention.

FIG. 12 is top plan view of an intermediate stage in the formation ofone of the test strip structures of FIG. 8, in accordance with anexemplary embodiment of the present invention.

FIG. 13 is top plan view of one of the test strip structures of FIG. 8,in accordance with an exemplary embodiment of the present invention.

FIG. 14 is a perspective view of a meter, in accordance with anexemplary embodiment of the present invention.

FIG. 15 is a perspective view of the meter of FIG. 14, with a removabledata storage device inserted in it, in accordance with an exemplaryembodiment of the present invention.

FIG. 16 is a perspective view of a strip connector in the meter of FIG.14, in accordance with an exemplary embodiment of the present invention.

FIG. 17 is an exploded perspective view of the removable data storagedevice of FIG. 15, in accordance with an exemplary embodiment of thepresent invention.

FIG. 18 is a flow chart illustrating a method of using a test strip or acheck strip, in accordance with en exemplary embodiment of the presentinvention.

FIG. 19 is a flow chart illustrating a method of using a check strip, inaccordance with an exemplary embodiment of the present invention.

FIG. 20 is a flow chart illustrating a method of using a test strip, inaccordance with an exemplary embodiment of the present invention.

FIG. 21 is a flow chart illustrating a method of using a test strip, inaccordance with an exemplary embodiment of the present invention.

FIG. 22 is a simplified schematic diagram of the electronics of themeter of FIG. 14, in accordance with an exemplary embodiment of thepresent invention.

FIG. 23 is a simplified schematic diagram of the electrical connectionsbetween the meter of FIG. 14 and the electrodes of the test strip ofFIG. 1, in accordance with an exemplary embodiment of the presentinvention.

FIG. 24 is a simplified schematic diagram of the electrical connectionsbetween the meter of FIG. 14 and the auto-on conductor of the test stripof FIG. 1, in accordance with an exemplary embodiment of the presentinvention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In accordance with a preferred embodiment, a system for measuring aglucose level in a blood sample includes a test strip and a meter. Thesystem may also include a removable data storage device associated witha lot of test strips. The removable data storage device stores data foruse by the meter, such as calibration coefficients for test strips fromthat lot. The system may also include a check strip that the user mayinsert into the meter to check that the meter is functioning properly.

The test strip includes a sample chamber or other testing zone where theblood sample is tested. The blood sample may reach the testing zonethrough an opening in the proximal end of the test strip. The testingzone may be vented through a porous cover or other venting structure.The test strip may include a tapered section that is narrowest at theproximal end, in order to make it easier for the user to locate theopening and apply the blood sample.

A working electrode, a counter electrode, a fill-detect electrode, and afill-detect anode are disposed so as to be able to measure at least oneelectrical characteristic of the blood sample in the testing zone. Areagent layer is disposed in the testing zone and preferably covers atleast the working electrode. The reagent layer may include an enzyme,such as glucose oxidase, and a mediator, such as potassium ferricyanide.The test strip has, near its distal end, a plurality of electricalcontacts that are electrically connected to the electrodes viaconductive traces. The test strip also has near its distal end anauto-on conductor, which may be electrically isolated from theelectrodes.

The meter may be battery powered and may stay in a low-power sleep modewhen not in use in order to save power. When the test strip is insertedinto the meter, the electrical contacts on the test strip contactcorresponding electrical contacts in the meter. In addition, the auto-onconductor bridges a pair of electrical contacts in the meter, causing acurrent to flow through the auto-on conductor. The current flow throughthe auto-on conductor causes the meter to wake up and enter an activemode. The meter also measures the voltage drop across the auto-onconductor and identifies the inserted strip as either a test strip or acheck strip based on the voltage drop. If the meter detects a checkstrip, it performs a check strip sequence. If the meter detects a teststrip, it performs a test strip sequence.

In the test strip sequence, the meter validates the working electrode,counter electrode, and fill-detect electrodes by confirming that thereare no low-impedance paths between any of these electrodes. If theelectrodes are valid, the meter indicates to the user that sample may beapplied to the test strip. The meter then applies a drop-detect voltagebetween the working and counter electrodes and detects the blood sampleby detecting a current flow between the working and counter electrodes(i.e., a current flow through the blood sample as it bridges the workingand counter electrodes). To detect that adequate sample is present inthe testing zone and that the blood sample has traversed the reagentlayer and mixed with the chemical constituents in the reagent layer, themeter applies a fill-detect voltage between the fill-detect electrodesand measures any resulting current flowing between the fill-detectelectrodes. If this resulting current reaches a sufficient level withina predetermined period of time, the meter indicates to the user thatadequate sample is present and has mixed with the reagent layer.

The meter waits for an incubation period of time after initiallydetecting the blood sample, to allow the blood sample to react with thereagent layer. Then, during a measurement period, the meter applies anassay voltage between the working and counter electrodes and takes oneor more measurements of the resulting current flowing between theworking and counter electrodes. The assay voltage is near the redoxpotential of the chemistry in the reagent layer, and the resultingcurrent is related to the glucose level in the blood sample. The metercalculates the glucose level based on the measured current and oncalibration data that the meter previously downloaded from the removabledata storage device associated with the test strip and stored in themeter's memory. The meter then displays the calculated glucose level tothe user.

1. Test Strip Configuration

With reference to the drawings, FIGS. 1, 2, and 3 show a test strip 10,in accordance with an exemplary embodiment of the present invention.Test strip 10 preferably takes the form of a generally flat strip thatextends from a proximal end 12 to a distal end 14. Preferably, teststrip 10 is sized for easy handling. For example, test strip 10 may beabout 1⅜ inches along its length (i.e., from proximal end 12 to distalend 14) and about 5/16 inches wide. However, proximal end 12 may benarrower than distal end 14. Thus, test strip 10 may include a taperedsection 16, in which the full width of test strip 10 tapers down toproximal end 12, making proximal end 12 narrower than distal end 14. Asdescribed in more detail below, the user applies the blood sample to anopening in proximal end 12 of test strip 10. Thus, providing taperedsection 16 in test strip 10, and making proximal end 12 narrower thandistal end 14, may help the user to locate the opening where the bloodsample is to be applied and may make it easier for the user tosuccessfully apply the blood sample to test strip 10.

As best shown in FIG. 3, test strip 10 may have a generally layeredconstruction. Working upward from the lowest layer, test strip 10 mayinclude a base layer 18 extending along the entire length of test strip10. Base layer 18 is preferably composed of an electrically insulatingmaterial and has a thickness sufficient to provide structural support totest strip 10. For example, base layer 18 may be polyester that is about0.014 inches think.

Disposed on base layer 18 is a conductive pattern 20. Conductive pattern20 includes a plurality of electrodes disposed on base layer 18 nearproximal end 12, a plurality of electrical contacts disposed on baselayer 18 near distal end 14, and a plurality of conductive traceselectrically connecting the electrodes to the electrical contacts. In apreferred embodiment, the plurality of electrodes includes a workingelectrode 22, a counter electrode 24, which may include a first section25 and a second section 26, a fill-detect anode 28, and a fill-detectcathode 30. Correspondingly, the electrical contacts may include aworking electrode contact 32, a counter electrode contact 34, afill-detect anode contact 36, and a fill-detect cathode contact 38. Theconductive traces may include a working electrode trace 40, electricallyconnecting working electrode 22 to working electrode contact 32, acounter electrode trace 42, electrically connecting counter electrode 24to counter electrode contact 34, a fill-detect anode trace 44electrically connecting fill-detect anode 28 to fill-detect contact 36,and a fill-detect cathode trace 46 electrically connecting fill-detectcathode 30 to fill-detect cathode contact 38. In a preferred embodiment,conductive pattern 20 also includes an auto-on conductor 48 disposed onbase layer 18 near distal end 14.

A dielectric layer 50 may also be disposed on base layer 18, so as tocover portions of conductive pattern 20. Preferably, dielectric layer 50is a thin layer (e.g., about 0.0005 inches thick) and is composed of anelectrically insulating material, such as silicones, acrylics, ormixtures thereof. Preferably, dielectric layer 50 is also hydrophilic.Dielectric layer 50 may cover portions of working electrode 22, counterelectrode 24, fill-detect anode 28, fill-detect cathode 30, andconductive traces 40-46, but preferably does not cover electricalcontacts 32-38 or auto-on conductor 48. For example, dielectric layer 50may cover substantially all of base layer 18, and the portions ofconductive pattern 20 thereon, from a line just proximal of contacts 32and 34 all the way to proximal end 12, except for a slot 52 extendingfrom proximal end 12. In this way, slot 52 may define an exposed portion54 of working electrode 22, exposed portions 56 and 58 of sections 25and 26 of counter electrode 24, an exposed portion 60 of fill-detectanode 28, and an exposed portion 62 of fill-detect cathode 30. As shownin FIG. 2, slot 52 may have different widths in different sections,which may make exposed portions 60 and 62 of fill-detect electrodes 28and 30 wider than exposed portions 54, 56, and 58 of working electrode22 and counter electrode sections 25 and 26.

The next layer in test strip 10 may be a dielectric spacer layer 64disposed on dielectric layer 50. Dielectric spacer layer 64 is composedof an electrically insulating material, such as polyester. Dielectricspacer layer 64 may have a length and width similar to that ofdielectric layer 50 but may be substantially thicker, e.g., about 0.005inches thick. In addition, spacer 64 may include a slot 66 that issubstantially aligned with slot 52. Thus, slot 66 may extend from aproximal end 68, aligned with proximal end 12, back to a distal end 70,such that exposed portions 54-62 of working electrode 22, counterelectrode 24, fill-detect anode 28, and fill-detect cathode 30 arelocated in slot 66.

A cover 72, having a proximal end 74 and a distal end 76, may beattached to dielectric spacer layer 64 via an adhesive layer 78. Cover72 is composed of an electrically insulating material, such aspolyester, and may have a thickness of about 0.004 inches. Preferably,cover 72 is transparent.

Adhesive layer 78 may include a polyacrylic or other adhesive and have athickness of about 0.0005 inches. Adhesive layer 78 may consist of afirst section 80 and a second section 82 disposed on spacer 64 onopposite sides of slot 66. A break 84 in adhesive layer 78 betweensections 80 and 82 extends from distal end 70 of slot 66 to an opening86. Cover 72 may be disposed on adhesive layer 78 such that its proximalend 74 is aligned with proximal end 12 and its distal end 76 is alignedwith opening 86. In this way, cover 72 covers slot 66 and break 84.

Slot 66, together with base layer 18 and cover 72, defines a samplechamber 88 in test strip 10 for receiving a blood sample formeasurement. Proximal end 68 of slot 66 defines a first opening insample chamber 88, through which the blood sample is introduced intosample chamber 88. At distal end 70 of slot 66, break 84 defines asecond opening in sample chamber 88, for venting sample chamber 88 assample enters sample chamber 88. Slot 66 is dimensioned such that ablood sample applied to its proximal end 68 is drawn into and held insample chamber 88 by capillary action, with break 84 venting samplechamber 88 through opening 86, as the blood sample enters. Moreover,slot 66 is dimensioned so that the blood sample that enters samplechamber 88 by capillary action is about 1 microliter or less. Forexample, slot 66 may have a length (i.e., from proximal end 68 to distalend 70) of about 0.140 inches, a width of about 0.060 inches, and aheight (which may be substantially defined by the thickness ofdielectric spacer layer 64) of about 0.005 inches. Other dimensionscould be used, however.

A reagent layer 90 is disposed in sample chamber 88. Preferably, reagentlayer 90 covers at least exposed portion 54 of working electrode 22.Most preferably, reagent layer 90 also at least touches exposed portions56 and 58 of counter electrode 24. Reagent layer 90 includes chemicalconstituents to enable the level of glucose in the blood sample to bedetermined electrochemically. Thus, reagent layer 90 may include anenzyme specific for glucose, such as glucose oxidase, and a mediator,such as potassium ferricyanide. Reagent layer 90 may also include othercomponents, such as buffering materials (e.g., potassium phosphate),polymeric binders (e.g., hydroxypropyl-methyl-cellulose, sodiumalginate, microcrystalline cellulose, polyethylene oxide,hydroxyethylcellulose, and/or polyvinyl alcohol), and surfactants (e.g.,Triton X-100 or Surfynol 485).

With these chemical constituents, reagent layer 90 reacts with glucosein the blood sample in the following way. The glucose oxidase initiatesa reaction that oxidizes the glucose to gluconic acid and reduces theferricyanide to ferrocyanide. When an appropriate voltage is applied toworking electrode 22, relative to counter electrode 24, the ferrocyanideis oxidized to ferricyanide, thereby generating a current that isrelated to the glucose concentration in the blood sample.

As best shown in FIG. 3, the arrangement of the various layers in teststrip 10 may result in test strip 10 having different thicknesses indifferent sections. In particular, among the layers above base layer 18,much of the thickness of test strip 10 may come from the thickness ofspacer 64. Thus, the edge of spacer 64 that is closest to distal end 14may define a shoulder 92 in test strip 10. Shoulder 92 may define a thinsection 94 of test strip 10, extending between shoulder 92 and distalend 14, and a thick section 96, extending between shoulder 92 andproximal end 12. The elements of test strip 10 used to electricallyconnect it to the meter, namely, electrical contacts 32-38 and auto-onconductor 48, may all be located in thin section 94. Accordingly, theconnector in the meter may be sized so as to be able to receive thinsection 94 but not thick section 96, as described in more detail below.This may beneficially cue the user to insert the correct end, i.e.,distal end 14 in thin section 94, and may prevent the user frominserting the wrong end, i.e., proximal end 12 in thick section 96, intothe meter.

Although FIGS. 1-3 illustrate a preferred configuration of test strip10, other configurations could be used. For example, in theconfiguration shown in FIGS. 1-3, counter electrode 24 is made up twosections, a first section 25 that is on the proximal side of workingelectrode 22 and a second section 26 that is on the distal side ofworking electrode 22. Moreover, the combined area of the exposedportions 56 and 58 of counter electrode 24 is preferably greater thanthe area of the exposed portion 54 of working electrode 22. In thisconfiguration, counter electrode 24 effectively surrounds workingelectrode 22, which beneficially shields working electrode 22electrically. In other configurations, however, counter electrode 24 mayhave only one section, such as first section 25.

Different arrangements of fill-detect electrodes 28 and 30 may also beused. In the configuration shown in FIGS. 1-3, fill-detect electrodes 28and 30 are in a side-by-side arrangement. Alternatively, fill-detectelectrodes 28 and 30 may be in a sequential arrangement, whereby, as thesample flows through sample-chamber 88 toward distal end 70, the samplecontacts one of the fill-detect electrodes first (either the anode orthe cathode) and then contacts the other fill-detect electrode. Inaddition, although exposed portions 60 and 62 of fill-detect electrodes28 and 30 are wider than exposed portions 54, 56, and 58 of workingelectrode 22 and counter electrode sections 25 and 26 in the embodimentshown in FIG. 2, they may have the same or a narrower width in otherembodiments.

However they are arranged relative to each other, it is preferable forfill-detect electrodes 28 and 30 to be located on the distal side ofreagent layer 90. In this way, as the sample flows through samplechamber 88 toward distal end 70, the sample will have traversed reagentlayer 90 by the time it reaches fill-detect electrodes 28 and 30. Thisarrangement beneficially allows the fill-detect electrodes 28 and 30 todetect not only whether sufficient blood sample is present in samplechamber 88 but also to detect whether the blood sample has becomesufficiently mixed with the chemical constituents of reagent layer 90.Thus, if reagent layer 90 covers working electrode 22, as is preferable,then it is preferable to locate fill-detect electrodes 28 and 30 on thedistal side of working electrode 22, as in the configuration shown inFIG. 1-3. Other configurations may be used, however.

Different configurations of the sample chamber in the test strip arealso possible. For example, FIG. 4 shows an alternate embodiment, teststrip 100, in which the sample chamber is vented without the use of abreak in an adhesive layer. In test strip 100, spacer 64 includes avented slot 102 that defines the sample chamber. Slot 102 includes awide section 104, which may have a relatively uniform width, a taperedsection 106, which may have a rounded shape, and a narrow section 108,which may also have a rounded shape. The exposed portions of the workingand counter electrodes may be located in wide section 104 and theproximal end of tapered section 106, and the exposed portions of thefill-detect electrodes may be located in the distal end of taperedsection 106. Cover 72 is attached to spacer 64 (e.g., using an adhesive)so as to cover slot 102 except for a distal end of narrow section 108.In this way, narrow section 108 may vent the sample chamber defined byslot 102. In addition, the rounded shape of tapered section 106 mayallow the sample to flow through the sample chamber more smoothly anduniformly.

A vented slot need not have a rounded shape, however. For example, FIG.5 shows another alternate embodiment, test strip 110, in which thesample chamber is also vented without the use of a break in an adhesivelayer. In test strip 110, spacer 64 includes a vented slot 112 thatdefines the sample chamber. Slot 112 includes a wide section 114, whichmay have a relatively uniform width, and a narrow section 116, which mayalso have a relatively uniform width. The exposed portions of theworking, counter, and fill-detect electrodes may all be located in widesection 114, with the exposed portions of the fill-detect electrodeslocated at the distal end of wide section 114. Cover 72 is attached tospacer 64 (e.g., using an adhesive) so as to cover slot 112, except fora distal end of narrow section 116. In this way, narrow section 116 mayvent the sample chamber defined by slot 112.

In the foregoing approaches for venting the sample chamber or testingzone, i.e., using a break in an adhesive layer or leaving part of theslot in the spacer uncovered, cover 72 may be a provided as asubstantially non-porous sheet of material. For example, 3M™ HydrophilicPolyester Film 9971, a polyester film with a hydrophilic coating on theside that contacts the blood sample, could be used as cover 72. However,in an alternative approach, a porous cover may be disposed over thetesting zone. In this alternative approach, the testing zone may bevented through the porous cover, such that no other structure forventing the testing zone may be needed.

The porous cover could be provided as a mesh. For example, FIG. 6 showsa cross-sectional schematic view of a test strip with a mesh 118positioned over a testing zone 119 that is defined by a slot in spacer64. The slot in spacer 64 also defines an opening in the proximal end ofthe test strip, through which a blood sample may be drawn into testingzone 119 by capillary action. Mesh 118 could be attached to spacer 64,for example, by an adhesive. In exemplary embodiments, mesh 118 has poresizes in the range of 18 to 105 microns and has a thickness in the rangeof 60 to 90 microns. Preferably, mesh 118 is hydrophilic. For example,mesh 118 could be polyester, polyamide, or polypropylene that has beendipped in a detergent solution, such as dioctyl sulfosuccinate.

The use of mesh 118 can simplify certain aspects of the fabrication ofthe test strips by eliminating any need for other venting structures. Inparticular, as the blood sample enters testing zone 119, testing zone119 can be vented through mesh 118. However, in some cases, mesh 118could allow the blood sample, as well as air, to flow through it. Thus,a user may be able to apply the blood sample through mesh 118 instead ofthrough the opening in the proximal end of the test strip as intended.Applying the blood sample in this way could result in an incorrectglucose reading. In addition, mesh 118 may not necessarily seal thesides of testing zone 119, as shown in FIG. 6, thereby allowing blood tomove through mesh 118.

In another approach, a perforated sheet may be used as the porous cover.For example, FIG. 7 shows a cross-sectional view of a test strip with aperforated sheet 120 positioned over a testing zone 121 that is definedby a slot in spacer 64. The slot in spacer 64 also defines an opening inthe proximal end of the test strip, through which a blood sample may bedrawn into testing zone 121 by capillary action. Perforated sheet 120includes a plurality of holes 122 formed therethrough, for example, in aregular array. In an exemplary embodiment, holes 122 are each about0.005 inches in diameter and are spaced about 0.020 inches fromcenter-center. Perforated sheet 120 may be formed by starting with animperforate sheet of material, such as 3M™ Hydrophilic Polyester Film9971, and then forming holes 122 in it, for example, by laser drillingor mechanical punching. Preferably, perforated sheet 120 is hydrophilicon the side that contacts the blood sample.

As a blood sample enters testing zone 121, testing zone 121 can bevented through holes 122 in perforated sheet 120. Thus, using perforatedsheet 120 can, like using mesh 118, eliminate the need for other ventingstructures. However, perforated sheet 120 may provide certain advantagesover mesh 118. For example, perforated sheet 120 can seal the sides oftesting zone 121, thereby reducing the possibility of the blood sampleleaking out. In addition, using perforated sheet 120 rather than mesh118 may make it more difficult to apply the blood sample the wrong way,i.e., through the porous cover instead of the opening in the proximalend of the test strip.

Other configurations of test strip, for example, with otherconfigurations of electrodes and/or testing zone may also be used.

2. Method of Manufacturing Test Strips

FIGS. 8 through 13 illustrate an exemplary method of manufacturing teststrips. Although these figures show steps for manufacturing test strip10, as shown in FIGS. 1-3, it is to be understood that similar steps maybe used to manufacture test strips having other configurations, such asthe test strips shown in any of FIGS. 4 through 7.

With reference to FIG. 8, a plurality of test strips 10 may bemass-produced by forming an integrated structure 124 that includes aplurality of test strip structures 126 all on one sheet. The test stripstructures 126 may be arranged in an array that includes a plurality ofrows 128 (e.g., six rows), with each row 128 including a plurality oftest strip structures 126 (e.g., fifty test strip structures in eachrow). The plurality of test strips 10 may then be formed by separatingthe test strip structures 126 from each other. In a preferred separationprocess, each row 128 of test strip structures 126 is first punched outof integrated structure 124. This punching process may provide some ofthe outer shape of the test strips 10. For example, the tapered shape oftapered sections 16 of the test strips 10 may be formed in this punchingprocess. Next, a slitting process may be used to separate the test stripstructures 126 in each row 128 into individual test strips 10.

FIGS. 9 through 13 show only one test strip structure (either partiallyor completely fabricated), in order to illustrate various steps in apreferred method for forming the test strip structures 126. In thispreferred approach, the test strip structures 126 in integratedstructure 120 are all formed on a sheet of material that serves as baselayer 18 in the finished test strips 10. The other components in thefinished test strips 10 are then built up layer-by-layer on top of baselayer 18 to form the test strip structures 126. In each of FIGS. 9through 13, the outer shape of the test strip 10 that would be formed inthe overall manufacturing process is shown as a dotted line.

As shown in FIG. 9, the manufacturing process may begin by forming, foreach test strip structure, a first conductive pattern 130 on base layer18. First conductive pattern 130 may include electrical contacts 32-38,conductive traces 40-42, and auto-on conductor 48. First conductivepattern 130 may be formed by screen-printing a first conductive ink ontobase layer 18. The first conductive ink may be provided as a viscousliquid that includes particles of a conductive material, such asmetallic silver. For example, a preferred first conductive ink has acomposition of about 30-60 weight % metallic silver, about 5-10 weight %lamp black, about 30-60 weight % dipropylene glycol monomethyl ether,and other components, and is available from E.I. DuPont de Nemours &Co., Wilmington, Del., as “Membrane Switch Composition 5524.”

As shown in FIG. 10, a second conductive pattern 132 may then be formedon base layer 18. Second conductive pattern 132 may include workingelectrode 22, first section 25 and second section 26 of counterelectrode 24, fill-detect anode 28, and fill-detect cathode 30. Secondconductive pattern 132 may be formed by screen-printing a secondconductive ink onto base layer 18. The second conductive ink may beprovided as a viscous liquid that includes particles of a conductivematerial, such as graphite. The second conductive ink may have adifferent composition than the first conductive ink. In particular, thesecond conductive ink is preferably substantially of free of materials,such as silver, that can interfere with the chemistry of reagent layer90. A preferred second conductive ink has a composition of about 10-20weight % graphite, about 5-10 weight % lamp black, greater than 60weight % ethylene glycol diacetate, and about 5-10 weight % polymer, andis available from E.I. DuPont de Nemours & Co., Wilmington, Del., as“E100735-111.”

As shown in FIG. 11, dielectric layer 50 may then be formed on baselayer 18 so as to cover portions of first conductive pattern 130 andsecond conductive pattern 132. As shown in FIG. 11, dielectric layer 50may extend beyond the outline of a finished test strip 10 so as to covermultiple test strip structures being formed on base layer 18. Also asshown in FIG. 11, dielectric layer 50 may include a slot 134 thatdefines exposed portions 54, 56, 58, 60, and 62 of working electrode 22,first counter electrode section 25, second counter electrode section 26,fill-detect anode portion 28, and fill-detect cathode portion 30. Slot52 in test strip 10 corresponds to the part of slot 134 that remains intest strip 10 after the test strip structures are separated into teststrips. In this regard, slot 134 may include a wide section 135 to allowthe portions of fill-detect electrodes 28 and 30 left exposed by layer50 to be wider than the portions of working electrode 22 and counterelectrode 24 left exposed by layer 50.

In a preferred approach, dielectric layer 50 is hydrophilic and isapplied by screen-printing a dielectric material. A preferred dielectricmaterial comprises a mixture of silicone and acrylic compounds, such asthe “Membrane Switch Composition 5018” available from E.I. DuPont deNemours & Co., Wilmington, Del. Other materials could be used, however.

In the next step, dielectric spacer layer 64 may be applied todielectric layer 50, as illustrated in FIG. 12. Spacer 64 may be appliedto dielectric layer 50 in a number of different ways. In an exemplaryapproach, spacer 64 is provided as a sheet large enough andappropriately shaped to cover multiple test strip structures. In thisapproach, the underside of spacer 64 may be coated with an adhesive tofacilitate attachment to dielectric layer 50 and base layer 18. Portionsof the upper surface of spacer 64 may also be coated with an adhesive inorder to provide adhesive layer 78 in each of the test strips 10.Various slots may be cut into or punched out of spacer 64 to shape itbefore spacer layer 64 is applied to dielectric layer 50. For example,as shown in FIG. 12, spacer 64 may have a slot 136 for each test stripstructure and a slot 138 that extends over multiple test stripstructures. In addition, spacer 64 may include adhesive sections 140 and142, with break 84 therebetween, for each test strip structure beingformed. Spacer 64 is then positioned over base layer 18, as shown inFIG. 12, and laminated to base layer 18 and dielectric layer 50. Whenspacer 64 is appropriately positioned on base layer 18, exposedelectrode portions 54-62 are accessible through slot 136. Thus, slot 66in test strip 10 corresponds to that part of slot 136 that remains intest strip 10 after the test strip structures are separated into teststrips. Similarly, slot 138 in spacer 64 leaves contacts 32-38 andauto-on conductor 48 exposed after lamination.

Alternatively, spacer 64 could be applied in other ways. For example,spacer 64 may be injection molded onto base layer 18 and dielectric 50.Spacer 64 could also be built up on dielectric layer 50 byscreen-printing successive layers of a dielectric material to anappropriate thickness, e.g., about 0.005 inches. A preferred dielectricmaterial comprises a mixture of silicone and acrylic compounds, such asthe “Membrane Switch Composition 5018” available from E.I. DuPont deNemours & Co., Wilmington, Del. Other materials could be used, however.

Reagent layer 90 may then be applied to each test strip structure. In apreferred approach, reagent layer 90 is applied by micropipetting anaqueous composition onto exposed portion 54 of working electrode 22 andletting it dry to form reagent layer 90. A preferred aqueous compositionhas a pH of about 6 and contains 2 weight % polyvinyl alcohol, 0.1 Mpotassium phosphate, 0.05 weight % Triton X-100, 0.15 M potassiumferricyanide, 0.7% hydroxyethylcellulose (such as NATROSOL®), and about2500 units of glucose oxidase per mL. Alternatively, other methods, suchas screen-printing, may be used to apply the composition used to formreagent layer 90.

A transparent cover 72 may then be attached to adhesive layer 78. Asshown in FIG. 13, cover 72 (which is shown as transparent) may be largeenough to cover multiple test strip structures 122. Attaching cover 72may complete the formation of the plurality of test strip structures122. The plurality of test strip structures 122 may then be separatedfrom each other to form a plurality of test strips 10, as describedabove.

3. The Meter and Removable Data Storage Device

To measure the glucose level in a blood sample, a test strip (e.g., teststrip 10, test strip 100, or test strip 110) is preferably used with ameter 200, as shown in FIGS. 14 and 15. Preferably, meter 200 has a sizeand shape to allow it to be conveniently held in a user's hand while theuser is performing the glucose measurement. Meter 200 may include afront side 202, a back side 204, a left side 206, a right side 208, atop side 210, and a bottom side 212. Front side 202 may include adisplay 214, such as a liquid crystal display (LCD). Bottom side 212 mayinclude a strip connector 216 into which the test strip is inserted toconduct a measurement.

Left side 206 of meter 200 may include a data connector 218 into which aremovable data storage device 220 may be inserted, as described in moredetail below. Top side 210 may include one or more user controls 222,such as buttons, with which the user may control meter 200. Right side208 may include a serial connector (not shown).

FIG. 16 shows a preferred embodiment of strip connector 216 in moredetail. Strip connector 216 includes a channel 230 with a flared opening231 for receiving a test strip. Tabs 232 and 234 hang over the left andright sides, respectively, of channel 230 at a predetermined height.This predetermined height is set to allow distal end 14 (in thin section94), but not proximal end 12 (in thick section 96), to be inserted intostrip connector 216. In this way, the user may be prevented fromimproperly inserting the test strip into strip connector 216.

Electrical contacts 236 and 238 are disposed in channel 230 behind tabs232 and 234, and electrical contacts 240-246 are disposed in channel 230behind electrical contacts 236 and 238. When distal end 14 of the teststrip is properly inserted into strip connector 216, electrical contacts236-246 contact electrical contacts 32-38 and auto-on conductor 48 toelectrically connect the test strip to meter 200. In particular,electrical contacts 236 and 238 contact electrical contacts 32 and 34,respectively, to electrically connect working electrode 22 and counterelectrode 24 to meter 200. Electrical contacts 240 and 242 contactelectrical contacts 36 and 38, respectively, to electrically fill-detectelectrodes 28 and 30 to meter 200. Finally, electrical contacts 244 and246 electrically connect auto-on conductor 48 to meter 200.

Meter 200 may use data from removable data storage device 220 tocalculate glucose levels in blood samples measured by meter 200.Specifically, data storage device 220 may be associated with a lot oftest strips and may store one or more parameters that meter 200 may usefor that lot. For example, data storage device 220 may store one or morecalibration parameters that meter 200 may use to calculate the glucoselevel from an averaged current measurement. The calibration parametersmay include temperature corrections. Data storage device 220 may alsostore other information related to the lot of test strips and the meter,such as a code identifying the brand of test strips, a code identifyingthe model of meter to be used, and an expiration date for the lot oftest strips. Data storage device 220 may also store other informationused by meter 200, such as the duration of the fill timer and theincubation timer, the voltages to use for the “Drop Level 1,” “Fill,”and “Assay Excitation Level 2” voltages, one or more parameters relatingto the number of current measurements to make, and one or moreparameters specifying how the meter should average the currentmeasurements, as described in more detail below. Data storage device 220may also store one or more checksums of the stored data or portions ofthe stored data.

In a preferred approach, before a given lot of test strips is used withmeter 200, the removable data storage device 220 associated with thatgiven lot is first inserted into data connector 218. Meter 200 may thenload the relevant data from data storage device 220 into an internalmemory when a test strip is inserted into strip connector 216. With therelevant data stored in its internal memory, meter 200 no longer needsdata storage device 220 to measure glucose levels using test strips inthe given lot. Thus, removable data storage device 220 may be removedfrom meter 200 and may be used to code other meters. If data storagedevice 220 is retained in meter 200, meter 200 may no longer access itbut instead use the data stored in its internal memory.

With reference to FIG. 17, removable data storage device 220 may includea memory chip 250 mounted on a circuit board 252, which, in turn, ismounted to a carrier 254. Memory chip 250 stores the data in apredetermined format. Preferably, memory chip 250 includes anon-volatile memory, so as to retain the stored data when un-powered.For example, memory chip 250 may be an electronically erasableprogrammable read only memory (EEPROM) chip. Such EEPROM chips cantypically be written to many times (e.g., one million write cycles, ormore) so that it does not wear out over the life cycle of usage.

Memory chip 250 may be electrically connected to a plurality ofelectrical contacts on circuit board 252. These electrical contacts mayinclude a voltage supply contact 256, a ground contact 258, a datainput/output contact 260, and a clock contact 262. In this way, when theappropriate voltage is applied to voltage supply 256, relative to groundcontact 258, data may be synchronously read from or written to memorychip 250 using data input/output contact 260 and clock contact 262. Asdescribed in more detail below, ground contact 258 may be longer thanthe other electrical contacts 256, 260, and 262, for greaterreliability.

Carrier 254 may be made out of a material such as plastic and mayinclude a distal end 264 and a proximal end 266. Distal end 264 isintended to be inserted into data connector 218. Proximal end 266 mayinclude a flange 268 to allow a user's fingers to grip removable datastorage device 220 for either insertion into or removal from dataconnector 218. Carrier 254 may include an opening 270 through whichelectrical contacts 256-262 are accessible. Thus, when data storagedevice 220 is properly inserted into data connector 218, electricalcontacts 256-262 on circuit board 252 contact corresponding electricalcontacts 272-278 (shown in FIG. 14), respectively, in data connector218. In this way, meter 200 may become electrical connected to memorychip 250 to read the data stored therein.

Carrier 254 and data connector 218 may be “keyed” so that removable datastorage device 220 may be inserted into connector 218 in only oneorientation. For example, carrier 254 may include a wedge-shaped corner282 and connector 218 may include a wedge-shaped opening 284 forreceiving wedge-shaped corner 282. As a result, data storage device 220may fit into data connector 218 only when oriented so that wedge-shapedcorner 282 is received in wedge-shaped opening 284. Beneficially, thiskeying may cue the user as to the proper insertion orientation and mayprevent damage that could be caused by improper insertion.

Another feature of removable data storage device 220 that may enhanceits reliability is the greater length of ground contact 258.Specifically, circuit board 252 is mounted to carrier 254 such thatground contact 258 extends closer to distal end 264 (i.e., the endinserted into data connector 218) than the other electrical contacts256, 260, and 262. As a result, ground contact 258 is the firstelectrical contact on circuit board 252 to make electrical contact withmeter 200 when data storage device 220 is inserted into data connector218 and the last electrical contact to break electrical contact withmeter 200 when data storage device 220 is removed. This prevents memorychip 250 from being powered in an unintended operating mode that may notbe reliable, e.g., the supply voltage from meter 200 being applied tomemory chip 250 through voltage supply contact 256 without memory chip250 also being connected to ground through ground contact 258.

4. The Use of the Test Strip with the Meter

In order to save power, meter 200 is preferably in a low power “sleep”mode most of the time. However, meter 200 may “wake up” and enter anactive mode when certain situations occur. For example, actuating one ormore of the user controls 222 may cause meter 200 to wake up, as mayattempting to use serial port 416 for data transfer. Preferably,inserting either a test strip (e.g., test strip 10, test strip 100, ortest strip 110) or a check strip into meter 200 also wakes it up. Meter200 may then determine whether the inserted strip is a test strip or acheck strip. The flow chart of FIG. 18 illustrates this process.

At first, meter 200 is in a low power sleep mode, as indicated by step300. Then, either a test strip or check strip is inserted into meter200, as indicated by step 302. The insertion causes the auto-onconductor on the strip (e.g., auto-on conductor 48 on test strip 10) tobridge auto-on contacts 244 and 246 in meter 200. As a result, anauto-on current starts to flow through auto-on contacts 244 and 246 andthrough the auto-on conductor. This auto-on current causes meter 200 towake up and enter an active mode, as indicated by step 304.

In this active mode, meter 200 measures the voltage drop across theauto-on conductor, as indicated by step 306. In a preferred approach,the resistance of the auto-on conductors in test strips is significantlydifferent than in check strips. Thus, meter 200 may determine whetherthe strip inserted into it is a test strip or a check strip based on theauto-on voltage drop. For example, the auto-on conductors in test stripsmay have a substantially lower resistance than in check strips.Accordingly, meter 200 may compare the auto-on voltage drop to apredetermined threshold value, as indicated by step 308. If the auto-onvoltage drop is less than the predetermined threshold value, then meter200 identifies the strip as a test strip and performs a test stripsequence, as indicated by step 310. On the other hand, if the auto-onvoltage drop is greater than the predetermined threshold value, thenmeter 200 identifies the strip as a check strip and performs a checkstrip sequence, as indicated by step 312.

The flowchart of FIG. 19 illustrates a preferred check strip sequence. Acheck strip may have electrical contacts near its distal end (inaddition to the auto-on conductor) that are similar to electricalcontacts 32-38 on the test strip, except that the electrical contacts onthe check strip may be connected to resistors, with predeterminedresistances, rather than to actual electrodes. Thus, when a check stripis inserted into meter 200, electrical contacts 236 and 238 may contact“working electrode” and “counter electrode” contacts on the check stripthat are actually connected via a first resistor in the check strip.Similarly, electrical contacts 240 and 242 may contact “fill-detect”contacts on the check strip that are actually connected via a secondresistor in the check strip.

As summarized in FIG. 19, meter 200 may perform the check strip sequenceby measuring the currents through the first and second resistors in thecheck strip to determine if the measured values fall within acceptableranges. If the measured current values do not fall within the acceptableranges, then there may be a problem with meter 200. Thus, meter 200 mayfirst measure the current through working and counter electrode contacts236 and 238 to obtain a measured current value through the firstresistor, as indicated by step 314. Meter 200 then determines if thismeasured current value is within the acceptable range, as indicated bystep 316. If the measured current value is not within the acceptablerange, then meter 200 indicates a failure status, as indicated by step318. To indicate the failure status, meter 200 may display a message oran icon on display 214 and/or provide some other user-discerniblefailure indication.

If the measured current through the first resistor is within theacceptable range, then meter 200 may also measure the current throughfill-detect electrode contacts 240 and 242 to obtain a measured currentvalue through the second resistor, as indicated by step 320. Then, meter200 determines whether this measured current value is within anacceptable range, as indicated by step 322. If the measured currentvalue is not within the acceptable range, then meter 200 indicates afailure status, as indicated by step 324. If the measured current valueis within the acceptable range, then meter 200 may indicate anoperational status. For example, meter 200 may display an “OK” icon ondisplay 214.

As noted above, if the meter 200 detects a test strip, then meter 200performs a test strip sequence. As a first phase of the test stripsequence, meter 200 may validate the working, counter, and fill-detectelectrodes by determining whether the impedances between them aresufficiently high. This process is illustrated in the flow chart of FIG.20.

As indicated by step 328, meter 200 may apply a predetermined firstvalidation voltage, e.g., the “Drop Level 1” voltage, between workingand counter electrodes 22 and 24 and measure any resulting currentflowing through working electrode 22. The first validation voltageshould result in little or no current, because there should not be alow-impedance pathway between working electrode 22 and counter electrode24. Thus, meter 200 may check whether the resulting current is below amaximum allowable value, as indicated by step 330. If the resultingcurrent is above the maximum value, then meter may indicate a failurestatus, as indicated by step 332.

Otherwise, meter 200 may proceed with the test strip sequence and applya predetermined second validation voltage, e.g., the “Fill” voltage,across fill-detect electrodes 28 and 30 and measure any resultingcurrent flowing through fill-detect anode 28, as indicated by step 334.Meter 200 may store this current measurement so that it can be used insubsequent measurements, as described in more detail below. The secondvalidation voltage should result in little or no current, because thereshould not be any low-impedance pathways between any of the electrodes.However, electronic components, such as amplifiers, in meter 200 mayproduce small offset currents that are measured in step 334. Meter 200may check whether the current measurement of step 334 is below a maximumallowable value, as indicated by step 336. If the current measurement isabove the maximum value, then meter 200 may indicate a failure status,as indicated by step 338. Otherwise, meter 200 may indicate that a bloodsample may be applied to the test strip. For example, meter 200 maydisplay a message or an icon on display 214 and/or provide some otheruser-discernible indication.

Meter 200 may perform the measurement of step 334 at the same time itperforms the measurement of step 328. Thus, meter 200 may apply the“Drop Level 1” voltage between working and counter electrodes 22 and 24,measuring any resulting current through working electrode 22, while atthe same time applying the “Fill” voltage between fill-detect electrodes28 and 30 and measuring any resulting current through fill-detect anode28.

If the electrodes are validated, meter 200 may then proceed with theprocess illustrated in the flow chart of FIG. 21. To detect when theuser applies the blood sample, meter 200 applies “Drop Level 1” voltageacross working electrode 22 and counter electrode 24 and measures anyresulting current flowing between these electrodes, as indicated by step342. Preferably, the “Drop Level 1” voltage is less than the redoxpotential of the chemistry used in reagent layer 90. At step 344, theuser applies a blood sample to the test strip. More particularly, theuser may apply the blood sample to the opening of sample chamber 88 atproximal end 12, as shown in FIG. 3. As noted above, sample chamber 88is dimensioned to draw the blood sample into it by capillary action. Asthe blood sample moves into sample chamber 88, it will eventually bridgeworking electrode 22 and counter electrode 24, thereby providing anelectrically conductive pathway between them. Thus, meter 200 determinesthat a blood sample is present in sample chamber 88 when the resultingcurrent reaches a predetermined threshold value or series of thresholdvalues with an overall positive magnitude change, as indicated by step346. When meter 200 detects the blood sample in this way, meter 200disconnects working and counter electrodes 22 and 24, putting them in ahigh impedance state relative to fill-detect electrodes 28 and 30, andmeter 200 starts a fill timer and an incubation timer, as indicated bystep 348. Before meter 200 puts working and counter electrodes 22 and 24in the high impedance state, meter 200 may first ground them todischarge stored charges.

The fill timer sets a time limit for the blood sample to traversereagent layer 90 and reach fill-detect electrodes 28 and 30. Theincubation timer sets a delay period to allow the blood sample to reactwith reagent layer 90. Once meter 200 starts the fill timer running,meter 200 applies a voltage, the “Fill” voltage, between fill-detectelectrodes 28 and 30 and measures the resulting current flowing betweenthese electrodes, as indicated by step 350. Meter 200 may subtract fromthis measured current the current measurement from step 334 to obtain anadjusted current. As indicated by step 352, meter 200 checks whether thecurrent (or adjusted current) reaches a predetermined threshold value ora series of thresholds with an overall positive magnitude change beforethe fill timer elapses. Preferably, the current threshold(s) are set sothat meter 200 can determine whether sufficient sample has reachedfill-detect electrodes 28 and 30 and whether the sample has become mixedwith the chemical constituents in reagent layer 90.

If the current (or adjusted current) does not reach the required value,then there may be some problem with the test strip. For example, theremay be a blockage in sample chamber 88. There may be an inadequateamount of sample. There may be no reagent layer, or the chemicalconstituents reagent layer may have failed to mix with the blood sample.Any of these problems may make the glucose measurement unreliable.Accordingly, if the fill timer elapses without a sufficient current (oradjusted current) through fill-detect electrodes 28 and 30, meter 200may indicate a failure status, as indicated by step 354. Meter 200 mayindicate this failure status by displaying an error message or icon ondisplay 214 and/or by providing some other user-discernible indication.The duration of the fill timer may, for example, be in the range of 2 to6 seconds.

If however, meter 200 detects sufficient current (or adjusted current)through fill-detect electrodes 28 and 30 before the fill timer elapses,then meter 200 may proceed with the glucose measurement process. Asindicated by step 356, meter 200 may provide an indication to the userthat meter 200 has detected adequate sample mixed with the chemicalconstituents of reagent layer 90. For example, meter 200 may beep,display a message or icon on display 214, or provide some otheruser-discernible indication. Preferably, meter 200 also disconnectsfill-detect electrodes 28 and 30, bringing them to a high impedancestate relative to working electrode 22 and counter electrode 24. Meter200 may ground fill-detect electrodes 28 and 30 before putting them intothe high impedance state in order to discharge stored charges. Meter 200then waits for the incubation timer to elapse, as indicated by step 358,in order to allow sufficient time for the blood sample to react withreagent layer 90. The incubation timer may, for example, take about 2seconds to about 10 seconds to elapse, depending on the implementation.In a preferred embodiment, the incubation timer lasts about 5 seconds.

When the incubation timer elapses, meter 200 applies the “AssayExcitation Level 2” voltage between working electrode 22 and counterelectrode 24 and measures the resulting current flowing between theseelectrodes, as indicated by step 360. Preferably, meter 200 measures theresulting current at a fixed sampling rate throughout a measurementperiod, to obtain a plurality of current measurements. The measurementperiod may last from about 5 seconds to about 15 seconds, depending onthe implementation. In a preferred embodiment, the measurement periodlasts about 5 seconds.

Meter 200 then determines the glucose level in the blood sample from thecurrent measurements, as indicated by step 362. In a preferred approach,meter 200 may average the current measurements to obtain an averagecurrent value at a predetermined point of time during the measurementperiod. Meter 200 may then use the calibration data obtained fromremovable data storage device 220 and stored in its internal memory tocalculate the glucose level from the average current value. Meter 200may also take a temperature reading and use the temperature reading tocorrect the measured glucose level for temperature dependence. Inaddition, meter 200 may check the validity of the current measurementsby checking that the measured current decreases over time, as expected.

For example, in a preferred embodiment, meter 200 may take apredetermined number of current measurements (m₁ . . . m_(M)) in 0.1second time intervals. The predetermined number, M, may, for example,range from 50 to 150, and it may be a parameter specified in removabledata storage device 220. The meter may then average every n currentmeasurements to provide a plurality of data points (d₁ . . . d_(N)).Thus, if n is equal to 3, the meter would calculate d₁ by averaging m₁,m₂, and m₃, and would calculated d₂ by averaging m₂, m₃, and m₄. Theaveraging parameter, n, may be a parameter specified in removable datastorage device 220. One of the data points may then be selected as thecenter point for another level of averaging, in which the meter averagestogether the data points around and including the center point toprovide a meter reading, X. Thus, if d₂ is selected as the center point,then the meter may average d₁, d₂, and d₃ together to calculate themeter reading, X. Removable data storage device 220 may store aparameter that specifies which of the data points to use as the centerpoint for calculating the meter reading, X. Meter 200 then calculatesthe glucose level, Y, from the meter reading, X, and one or morecalibration parameters, which may be specified in removable data storagedevice 220. For example, in an exemplary embodiment, meter 200 may usethree calibration parameters, a, b, and c, to calculate Y, using theexpression a+bX+cX². Alternatively, different expressions, which mayinclude different terms and/or different numbers of calibrationparameters, may be used to calculate Y. For example, in anotherexemplary embodiment, Y may be calculated using the expressiona+bX+cX²+d/X. In some cases, data storage device 220 may specify whatexpression to use to calculate Y in addition to what calibrationparameters to use.

The glucose level, Y, calculated in this way may not be temperaturecorrected, however. To correct for temperature, meter 200 may apply oneor more temperature correction parameters, which may be specified inremovable data storage device 220. For example, in a preferredembodiment, the temperature-corrected glucose level may be calculatedfrom the expression A+BT+CYT+DY, where A, B, C, and D are temperaturecorrection parameters and T is a measured temperature. The calibrationparameters A, B, C, and D may be specified in removable data storagedevice 220. In other embodiments, the temperature correction may useonly a single parameter, S, which may be specified in removable datastorage device 220. For example, the temperature-corrected glucose levelmay be calculated from the expression Y/[(1+S(T−21)].

If the current measurements appear valid, then meter 200 displays theglucose level, typically as a number, on display 214, as indicated bystep 364. Meter 200 may also store the measured glucose level, with atimestamp, in its internal memory.

5. Meter Electronics

FIG. 22 shows, in simplified form, the electronic components of meter200, in accordance with a preferred embodiment. Meter 200 may include amicrocontroller 400 that controls the operation of meter 200 inaccordance with programming, which may be provided as software and/orfirmware. Microcontroller 400 may include a processor 402, a memory 404,which may include read-only memory (ROM) and/or random access memory(RAM), a display controller 406, and one or more input/output (I/O)ports 408. Memory 404 may store a plurality of machine languageinstructions that comprises the programming for controlling theoperation of meter 200. Memory 404 may also store data. Processor 402executes the machine language instructions, which may be stored inmemory 404 or in other components, to control microcontroller 400 and,thus, meter 200. In particular, processor 402 may execute the storedmachine language instructions so that meter 200 performs the functionssummarized in the flowcharts of FIGS. 18-21 and described above.

Microcontroller 400 may also include other components under the controlof processor 402. For example, microcontroller 400 may include a displaycontroller 406 to help processor 402 control display 214. In a preferredembodiment, display 214 is an LCD and display controller 406 is an LCDdriver/controller. Microcontroller may also include I/O ports 408, whichenable processor 402 to communicate with components external tomicrocontroller 400. Microcontroller 400 may also include one or moretimers 410. Processor 402 may use timers 410 to measure the fill timeperiod, incubation time period, and other time periods described above.Microcontroller 400 may be provided as an integrated circuit, such asthe HD64F38024H, available from Hitachi.

Microcontroller 400 is preferably connected to components that provide auser interface. The components that make up the user interface of meter200 may include display 214, a beeper 412, and user controls 222.Microcontroller 400 may display text and/or graphics on display 214.Microcontroller may cause beeper 412 to beep, such as to indicate thatadequate sample (mixed with the chemistry of reagent layer 90) hasreached fill-detect electrodes 28 and 30, as described above.Microcontroller 400 may also be connected to other components, such asone or more light-emitting diodes (LEDs), to provide user-discernibleindications, which may be visible, audible, or tactile. Microcontroller400 may receive user input from user controls 222. In a preferredembodiment, user controls 222 consists of a plurality of discreteswitches. However, user controls 222 may also include a touch screen orother components with which a user can provide input to meter 200.

Microcontroller 400 may have access to one or more memories external toit, such as an EEPROM 414. In a preferred embodiment, microcontroller400 stores the measured glucose levels, and the times and dates theglucose measurements occurred, in EEPROM 414. By using user controls222, the user may also be able to cause microcontroller 400 to displayone or more of the glucose measurements stored in EEPROM 414 on display214. Microcontroller 400 may also be connected to a serial port 416,through which the user can access the glucose measurements stored inEEPROM 414. Microcontroller 400 may use a transmit line, “TX,” totransmit signals to serial port 416 and may use a receive line, “RX,” toreceive signals from serial port 416.

EEPROM 414 may also store the data from removable data storage device220. In this regard, FIG. 22 shows how electrical contacts 272-278 ofdata connector 216 are connected inside of meter 200. Contact 272 isconnected to a source of power, which may be through microcontroller400. In this way, microcontroller 400 can do “power management,”powering removable data storage device 220, through contact 272, onlywhen necessary, e.g., when downloading data from removable data storagedevice 220. Contact 274 is connected to ground. Contacts 276 and 278 areconnected to data input/output and clock outputs, respectively, ofmicrocontroller 400. In this way, microcontroller 400 may download thedata from data storage device 220, when connected to data connector 216,and store the data in EEPROM 414.

In a preferred embodiment, meter 200 also includes a data acquisitionsystem (DAS) 420 that is digitally interfaced with microcontroller 400.DAS 420 may be provided as an integrated circuit, such as the MAX1414,available from Maxim Integrated Products, Sunnyvale, Calif.

DAS 420 includes one or more digital-to-analog converters (DACs) thatgenerate analog voltages in response to digital data frommicrocontroller 400. In particular, DAS 420 includes “Vout1” and “FB1”terminals, which DAS 420 uses to apply analog voltages generated by afirst DAC to working electrode 22, when the test strip is inserted instrip connector 216. Similarly, DAS 420 includes “Vout2” and “FB2”terminals, which DAS 420 uses to apply analog voltages generated by asecond DAC to fill-detect anode 28, when a test strip is inserted instrip connector 216. The one or more DACs in DAS 420 generate analogvoltages based on digital signals provided by microcontroller 400. Inthis way, the voltages generated by the one or more DACs may be selectedby processor 402.

DAS 420 also includes one or more analog-to-digital converters (ADCs)with which DAS 420 is able to measure analog signals. As described inmore detail below, DAS 420 may use one or more ADCs connected to the“Vout1” and “Vout2” terminals to measure currents from working electrode22 and counter electrode 24, respectively, when a test strip is insertedin strip connector 216. DAS 420 may also include one or more otherterminals through which the ADCs may measure analog signals, such as the“Analog In1” and “Analog In2” terminals shown in FIG. 22. DAS 420 mayuse the “Analog In1” terminal to measure the voltage across the auto-onconductor in a test strip or check strip that is connected to stripconnector 216. The “Analog In2” terminal may be connected to athermistor, RT1, to enable DAS 420 to measure temperature. Inparticular, DAS 420 may supply a reference voltage, V_(ref), through avoltage divider that includes thermistor, RT1, and another resister,R_(d). DAS 420 may use the “Analog In2” terminal to measure the voltageacross thermistor, RT1. DAS 420 transfers the digital values obtainedfrom the one or more ADCs to microcontroller 400, via the digitalinterface between these components.

Preferably, DAS 420 has at least two modes of operation, a “sleep” orlow-power mode and an “active” or run mode. In the active mode, DAS 420has full functionality. In the sleep mode, DAS 420 has reducedfunctionality but draws much less current. For example, while DAS 420may draw 1 mA or more in the active mode, DAS 420 may draw onlymicroamps in the sleep mode. As shown in FIG. 22, DAS 420 may include“Wake-up1,” “Wake-up2,” and “Wake-up3” inputs. When appropriate signalsare asserted at any of these “Wake-up” terminals, DAS 420 may wake upfrom the sleep mode, enter the active mode, and wake up the rest ofmeter 200, as described in more detail below. In a preferred embodiment,the “Wake-up” inputs are active-low inputs that are internally pulled upto the supply voltage, Vcc. As described in more detail below, insertingthe auto-on conductor in either a test strip or check strip into stripconnector 216 causes the “Wake-up1” input to go low and, thereby,causing DAS 420 to enter the active mode. In addition, the “Wake-up2”input may be connected to one or more of user controls 222. In this way,the user's actuation of at least certain of user controls 222 causes DAS420 to enter the active mode. Finally, the “Wake-up3” input may beconnected to serial port 416, e.g., via receive line, “RX.” In this way,attempting to use serial port 416 for data transfer may wake up DAS 420and, hence, meter 200.

As shown in FIG. 22, DAS 420 includes several terminals that areconnected to microcontroller 400. DAS 420 includes one or more “DataI/O” terminals, through which microcontroller 400 may write digital datato and read digital data from DAS 420. DAS 420 also includes a “ClockIn” terminal that receives a clock signal from microcontroller 400 tocoordinate data transfer to and from the “Data I/O” terminals. DAS 420may also include a “Clock Out” terminal through which DAS 420 may supplya clock signal that drives microcontroller 400. DAS 420 may generatethis clock signal by using a crystal 422. DAS 420 may also generate areal time clock (RTC) using crystal 422.

DAS 420 may also include other terminals through which DAS 420 mayoutput other types of digital signals to microcontroller 400. Forexample, example DAS 420 may include a “Reset” terminal, through whichDAS 420 may output a signal for resetting microcontroller 400. DAS 420may also include one or more “Interrupt Out” terminals, which DAS 420may use to provide interrupt signals to microcontroller 400. DAS 420 mayalso include one or more “Data Ready” inputs that DAS 420 may use tosignal microcontroller 400 that DAS 420 has acquired data, such as froman analog-to-digital conversion, which is ready to be transferred tomicrocontroller 400.

As shown in FIG. 22, meter 200 may include a power source, such as oneor more batteries 424. A voltage regulator 426 may provide a regulatedsupply voltage, V_(CC), from the voltage supplied by batteries 424. Thesupply voltage, V_(CC), may then power the other components of meter200. In a preferred embodiment, voltage regulator 426 is a step-upDC-to-DC voltage converter. Voltage regulator 426 may be provided as anintegrated circuit and other components, such as an inductor,capacitors, and resistors. The integrated circuit may, for example, be aMAX1724, available from Maxim Integrated Products, Sunnyvale, Calif.

Preferably, voltage regulator 426 has a shutdown mode, in which itprovides only an unregulated output voltage. DAS 420 may include a“Shutdown” terminal through which DAS 420 may control voltage regulator426. In particular, when DAS 420 enters the sleep mode, DAS 420 mayassert a low level signal at its “Shutdown” terminal, causing voltageregulator 426 to enter the shutdown mode. When DAS 420 enters the activemode, it asserts a high level signal at its “Shutdown” terminal,allowing voltage regulator 426 to operate normally.

FIG. 22 also shows how electrical contacts 236-246 of strip connector216 are connected in meter 200. Contacts 236 and 238, which areelectrically connected to working electrode 22 and counter electrode 24,respectively, when the test strip is inserted in strip connector 216,are connected as follows. Contact 236, for working electrode 22, isconnected to the “FB1” terminal of DAS 420 and connected via a resistor,RF1, to the “Vout1” terminal of DAS 420. Contact 238, for counterelectrode 24, is connected to a switch 428. Switch 428 allows contact238 (and, hence, counter electrode 24) to be connected to ground or leftin a high impedance state. Switch 428 may be digitally controlled bymicrocontroller 400, as shown in FIG. 22. With counter electrode 24connected to ground, DAS 420 may use the “Vout1” and “FB1” terminals toapply voltages to working electrode 22 (relative to counter electrode24) and to measure the current through working electrode 22.

Contacts 240 and 242, which are electrically connected to fill-detectanode 28 and fill-detect cathode 30, respectively, when the test stripis inserted in strip connector 216, are connected as follows. Contact240, for fill-detect anode 28, is connected to the “FB2” terminal of DAS420 and connected via a resistor, RF2, to the “Vout2” terminal of DAS420. Contact 242, for fill-detect cathode 30, is connected to a switch430. Switch 430 allows contact 242 (and, hence, fill-detect cathode 30)to be connected to ground or left in a high impedance state. Switch 430may be digitally controlled by microcontroller 400, as shown in FIG. 22.With fill-detect cathode 30 connected to ground, DAS 420 may use the“Vout2” and “FB2” terminals to apply voltages to fill-detect anode 28(relative to fill-detect cathode 30) and to measure the current throughfill-detect anode 28.

Switches 428 and 430 may be single-pole/single-throw (SPST) switches,and they may be provided as an integrated circuit, such as the MAX4641,available from Maxim Integrated Products, Sunnyvale, California.However, other configurations for switches 428 and 430 could be used.

Contacts 244 and 246, which are electrically connected to the auto-onconductor when a test strip or check strip is inserted into stripconnector 216, are connected as follows. Contact 246 is connected toground or other reference potential. Contact 244 is connected to the“Analog In1” and “Wake-up1” terminals of DAS 420 and to microcontroller400. As described in more detail below, the presence of the auto-onconductor drives the “Wake-up1” terminal low, thereby waking up DAS 420and causing it to enter an active mode. DAS 420 uses the “Analog In1”terminal to measure the voltage across the auto-on conductor. By virtueof its connection to contact 244, microcontroller 400 is able todetermine whether the auto-on conductor is present, and, thus, whethereither a test strip or check strip is connected to strip connector 216.

FIG. 23 shows in greater detail the functional aspects of theconnections between meter 200 and electrodes 22, 24, 28, and 30, whenthe test strip is inserted in strip connector 216. As shown in FIG. 23,DAS 420 functionally includes an amplifier 440 for working electrode 22and an amplifier 442 for fill-detect anode 28. More particularly, theoutput of amplifier 440 is connected to working electrode 22, via the“Vout1” terminal and resistor, RFI, and the inverting input of amplifier440 is connected to working electrode 22, via the “FB1” terminal.Similarly, the output of amplifier 442 is connected to fill-detect anode28, via the “Vout2” terminal and resistor, RF2, and the inverting inputof amplifier 442 is connected to fill-detect anode 28, via the “FB2”terminal.

To generate selected analog voltages to apply to working electrode 22and fill-detect electrode 28, DAS 420 includes a first DAC 444 and asecond DAC 446, respectively. DAC 444 is connected to the non-invertinginput of amplifier 440, and DAC 446 is connected to the non-invertinginput of amplifier 442. In this way, amplifier 440 applies a voltage tothe “Vout1” terminal, such that the voltage at working electrode 22, assensed at the inverting input of amplifier 440, is essentially equal tothe voltage generated by DAC 444. Similarly, amplifier 442 applies avoltage to the “Vout2” terminal, such that the voltage at fill-detectelectrode 28, as sensed at the inverting input of amplifier 442, isessentially equal to the voltage generated by DAC 446.

To measure the currents through working electrode 22 and fill-detectanode 28, DAS 420 includes an ADC 448 and multiplexers (MUXes) 450 and452. MuXes 450 and 452 are able to select the inputs of ADC 448 fromamong the “Vout1,” “FB1,” “Vout2,” and “FB2” terminals. DAS 420 may alsoinclude one or more buffers and/or amplifiers (not shown) between ADC448 and MUXes 450 and 452. To measure the current through workingelectrode 22, MUXes 450 and 452 connect ADC 448 to the “Vout1” and “FB1”terminals to measure the voltage across resistor, RF1, which isproportional to the current through working electrode 22. To measure thecurrent through fill-detect electrode 28, MUXes 450 and 452 connect ADC448 to the “Vout2” and “FB2” terminals to measure the voltage acrossresistor, RF2, which is proportional to the current through fill-detectanode 28.

As noted above, meter 200 preferably includes switches 428 and 430 thatmay be used to bring counter electrode 24 and fill-detect cathode 30,respectively, into a high impedance state. It is also preferable formeter 200 to be able to bring working electrode 22 and fill-detect anode28 into a high impedance state as well. In a preferred embodiment, thismay be achieved by DAS 420 being able to bring terminals “Vout1,” “FB1,”“Vout2,” and “FB2” into high impedance states. Accordingly, DAS 420 mayeffectively include switches 454, 456, 458, and 460, as shown in FIG.23. Although switches 428, 430, and 454-460 may be SPST switches, asshown in FIG. 23, other types of switches, such as single pole-doublethrow (SPDT) switches, may be used, and the switches may be arranged inother ways, in order to provide meter 200 with the ability to select onepair of electrodes (either the working and counter electrode pair or thefill-detect electrode pair) and leave the other pair of electrodes in ahigh impedance state. For example, a pair of SPDT switches may be used,with one SPDT switch selecting which of working electrode 22 andfill-detect 28 to connect to DAS 420 and the other SPDT switch selectingwhich of counter electrode 24 and fill-detect cathode to connect toground. In other cases, meter 200 may not be configured to bring all ofthe electrodes into high impedance states. For example, in someembodiments, meter 200 may not include switch 428, with the result thatcounter electrode 24 is always connected to ground when the test stripis inserted in strip connector 216.

FIG. 24 shows in greater detail the functional aspects of theconnections between meter 200 and the auto-on conductor when either atest strip or a check strip is inserted in strip connector 216. As shownin FIG. 24, the auto-on conductor provides an effective resistance,Rauto, between contacts 244 and 246 of strip connector 216. Within meter200, contact 244 is connected to the source voltage, V_(cc), through aneffective resistance, R_(S). For example, the “Wake-up 1” terminal ofDAS 420, to which contact 244 is connected, may be internally pulled upto V_(cc), through an effective resistance, R_(S). Accordingly, wheneither a test strip or a check strip is inserted into strip connector216, such that the auto-on conductor bridges contacts 244 and 246, acurrent flows through the auto-on resistor and a voltage drop developsbetween contacts 244 and 246. The magnitude of this auto-on voltage dropdepends on the relative magnitudes of R_(auto) and R_(S). Preferably,R_(auto) is chosen sufficiently low for the test strips and checkstrips, relative to R_(S), such that the auto-on voltage is less thanthe logic low voltage (which may be about 0.8 volts) used in meter 200.It is also preferable for R_(auto) to be substantially different in teststrips and check strips, so that meter 200 may determine the strip typefrom the auto-on voltage drop. For example, if R_(S) is about 500 kΩ,then R_(auto) may be less than about 20 Ω in a test strip and may beapproximately 20 kΩ in a check strip. In this way, microcontroller 400may determine that either a test strip or check strip is inserted instrip connector 216 by sensing a logic low voltage at contact 244.

DAS 420 also senses the auto-on voltage drop and uses it to wake upmeter 200 and to determine the strip type, i.e., whether a test strip ora check strip has been inserted into strip connector 216. In the case ofa test strip, DAS 420 may also confirm that the test strip has beenproperly inserted into strip connector 216.

DAS 420 may include wake-up logic 462, which senses the voltage at the “Wake-up1” terminal, via one or more buffers and/or amplifiers, such asbuffer 464. DAS 420 also includes ADC 448, which can measure the voltageat the “Analog In 1” terminal, via one or more buffers and/oramplifiers, such as buffer 466. Although not shown in FIG. 24, MUXes 450and 452 may be connected between buffer 466 and ADC 448.

When no strip is present in strip connector 216, contact 244 (and, thus,the “Wake-up1” terminal) is at a high voltage, at or near V_(CC).However, when either a test strip or a check strip is inserted in stripconnector 216, the auto-on conductor drives the voltage at the“Wake-up1” terminal low, as described above. Wake-up logic 462 sensesthe voltage at the “Wake-up1” terminal going low and, in response,initiates a wake-up sequence to bring DAS 420 into an active mode. Aspart of this wake-up sequence, wake-up logic 462 may cause DAS 420 toassert a signal at its “Shutdown” terminal to turn on voltage regulator426. Wake-up logic 462 may also cause DAS 420 to generate signals towake up microcontroller 400. For example, wake-up logic 462 may causeDAS 420 to assert a clock signal through its “Clock Out” terminal, areset signal through its “Reset” terminal, and an interrupt signalthrough its “Interrupt Out” terminal to activate microcontroller 400.

Though not shown in FIG. 24, wake-up logic 462 may also sense thevoltages at the “Wake-up1” and “Wake-up2” terminals and, in response toa voltage at one of these terminals going low, may initiate a wake-upsequence similar to that described above.

When DAS 420 enters the active mode, it also determines the type ofstrip inserted into strip connector 216. In particular, ADC 448 measuresthe voltage at the “Analog In1” terminal. DAS 420 then reports themeasured voltage to microcontroller 400. Based on this information,microcontroller 400 then initiates either a test strip sequence or acheck strip sequence, as described above. Throughout either sequence,microcontroller 400 may periodically check the voltage at contact 244 tomake sure that the strip is still inserted in strip connector 216.Alternatively, an interrupt may notify microcontroller 400 of a voltageincrease at contact 244 caused by removal of the strip.

In this way, the auto-on voltage drop developed across the auto-onconductor performs several functions in meter 200. First, the auto-onvoltage wakes up meter 200 from a sleep mode to an active mode. Second,meter 200 determines the strip type from the magnitude of the auto-onvoltage. Third, the auto-on voltage lets meter 200 know that the stripis still inserted in strip connector 216, as meter 200 proceeds witheither the test strip or check strip sequence.

6. Conclusion

Preferred embodiments of the present invention have been describedabove. Those skilled in the art will understand, however, that changesand modifications may be made to these embodiments without departingfrom the true scope and spirit of the invention, which is defined by theclaims.

1. A test strip for measuring glucose in a blood sample, said test stripcomprising: a base layer, said base layer having a proximal end and adistal end, said proximal end being narrower than said distal end; atleast four electrodes disposed on said base layer, said at least fourelectrodes including a working electrode, a counter electrode, afill-detect anode, and a fill-detect cathode; a plurality of electricalcontacts disposed on said base layer, said plurality of electricalcontacts including a working electrode contact, a counter electrodecontact, a fill-detect anode contact, and a fill-detect cathode contact;a plurality of conductive traces disposed on said base layer, saidplurality of conductive traces electrically connecting said workingelectrode to said working electrode contact, said counter electrode tosaid counter electrode contact, said fill-detect anode to saidfill-detect anode contact, said fill-detect cathode to said fill-detectcathode contact; an auto-on conductor disposed on said base layer; afirst dielectric layer disposed on said base layer, said firstdielectric layer covering portions of said working electrode and saidcounter electrode, so as to define an exposed working electrode portionand an exposed counter electrode portion; a second dielectric layerdisposed on said base layer, said second dielectric layer having a slot,said working electrode, said counter electrode, said fill-detect anode,and said fill-detect cathode being disposed in said slot, said slothaving a proximal end and a distal end, said proximal end of said slotbeing aligned with said proximal end of said base layer; a reagent layerdisposed in said slot, said reagent layer including glucose oxidase anda mediator; and a porous cover disposed on said second dielectric layer,wherein said slot defines a testing zone for testing said blood sample,said slot being dimensioned to draw said blood sample in through saidproximal end of said slot by capillary action.
 2. The test strip ofclaim 1, wherein said porous cover comprises a mesh.
 3. The test stripof claim 1, wherein said porous cover comprises a perforated sheet. 4.The test strip of claim 1, wherein said counter electrode includes afirst section and a second section, said working electrode beingdisposed on said base layer between said first section and said secondsection.
 5. The test strip of claim 1, wherein said at least fourelectrodes are formed by a first conductive ink printed on said baselayer.
 6. The test strip of claim 5, wherein said first conductive inkcontains graphite.
 7. The test strip of claim 6, wherein said electricalcontacts, said conductive traces, and said auto-on conductor are formedby a second conductive ink printed on said base layer.
 8. The test stripof claim 7, wherein said second conductive ink contains silver.
 9. Thetest strip of claim 1, wherein said test strip has a thick section and athin section, said thick section including said proximal end, said thinsection including said distal end, said electrical contacts and saidauto-on conductor being located in said thin section.
 10. The test stripof claim 1, wherein said reagent layer covers said exposed workingelectrode portion.
 11. A test strip for testing a blood sample, saidtest strip comprising: a first substrate; a second substrate, saidsecond substrate defining a testing zone for testing said blood sample;at least four electrodes, disposed on said first substrate, formeasuring at least one electrical characteristic of said blood sample insaid testing zone, said at least four electrodes including a workingelectrode, a counter electrode, a fill-detect anode, and a fill-detectcathode; a plurality of electrical contacts disposed on said firstsubstrate and electrically connected to said at least four electrodes;and at least one auto-on electrical contact disposed on said firstsubstrate and electrically isolated from said at least four electrodes.12. The test strip of claim 11, further comprising: a reagent layerdisposed in said testing zone.
 13. The test strip of claim 11, furthercomprising: a cover disposed over said testing zone.
 14. The test stripof claim 13, wherein said cover is a porous cover.
 15. The test strip ofclaim 14, wherein said porous cover comprises a mesh.
 16. The test stripof claim 14, wherein said porous cover comprises a perforated sheet. 17.The test strip of claim 11, wherein said test strip has a proximal endand a distal end, wherein said second substrate defines an opening atsaid proximal end for receiving said blood sample.
 18. The test strip ofclaim 17, wherein said proximal end is narrower than said distal end.19. The test strip of claim 17, wherein said test strip has a thicksection and a thin section, said thick section including said proximalend, said thin section including said distal end.
 20. The test strip ofclaim 19, wherein said plurality of electrical contacts and said atleast one auto-on electrical contact are located in said thin section.21. A method of making a plurality of test strips, said methodcomprising: forming a plurality of test strip structures on aninsulating sheet, wherein each test strip structure is formed by: (a)forming a first conductive pattern on said insulating sheet, said firstconductive pattern including at least four electrodes, said at leastfour electrodes including a working electrode, a counter electrode, afill-detect anode, and a fill-detect cathode; (b) forming a secondconductive pattern on said insulating sheet, said second conductivepattern including a plurality of electrode contacts for said at leastfour electrodes, a plurality of conductive traces electricallyconnecting said at least four electrodes to said plurality of electrodecontacts, and an auto-on conductor; (c) applying a first dielectriclayer over portions of said working electrode and said counterelectrode, so as to define an exposed working electrode portion and anexposed counter electrode portion; (d) applying a second dielectriclayer to said first dielectric layer, said second dielectric layerdefining a slot, said working electrode, said counter electrode, saidfill-detect anode, and said fill-detect cathode being disposed in saidslot; (e) forming a reagent layer in said slot, said reagent layerincluding glucose oxidase and a mediator; and (f) attaching a porouscover to said second dielectric layer; and separating said plurality oftest strip structures into said plurality of test strips, each of saidtest strips having a proximal end and a distal end, with said slotextending to said proximal end, said proximal end being narrower thansaid distal end.
 22. The method of claim 21, wherein said porous covercomprises a mesh.
 23. The method of claim 21, wherein said porous covercomprises a perforated sheet.
 24. The method of claim 21, whereinforming a first conductive pattern on said insulating sheet comprises:printing a first conductive ink on said insulating sheet, said firstconductive ink containing graphite.
 25. The method of claim 24, whereinforming a second conductive pattern on said insulating sheet comprises:printing a second conductive ink on said insulating sheet, said secondconductive ink containing silver.
 26. A method of making a plurality oftest strips, said method comprising: forming a plurality of test stripstructures on one sheet, each of said test strip structures including:(a) a spacer defining a testing zone; (b) a plurality of electrodesformed on said sheet, including a working electrode, a counterelectrode, a fill-detect anode, and a fill-detect cathode; (c) aplurality of electrical contacts, formed on said sheet and electricallyconnected to said plurality of electrodes; and (d) at least one auto-onelectrical contact, formed on said sheet and electrically isolated fromsaid plurality of electrodes; and separating said test strip structuresinto said plurality of test strips.
 27. The method of claim 26, whereineach of said test strip structures further comprises: a cover disposedover said testing zone.
 28. The method of claim 27, wherein said coveris a porous cover.
 29. The method of claim 28, wherein said porous covercomprises a mesh.
 30. The method of claim 28, wherein said porous covercomprises a perforated sheet.
 31. The method of claim 26, wherein eachof said test strip structures includes a reagent layer disposed in saidtesting zone.
 32. The method of claim 26, wherein separating said teststrip structures into said plurality of test strips comprises: punchingsaid plurality of test strip structures to form a plurality of taperedtest strip structures, each of said tapered test strip structures havinga tapered section.
 33. The method of claim 32, wherein separating saidtest strip structures into said plurality of test strips furthercomprises: slitting said plurality of tapered test strip structures intosaid plurality of test strips.